This invention relates to a vehicle control, and in particular relates to the control of a vehicle provided with a generator and a vehicle drive motor.
In recent years, hybrid vehicles (HEV) comprising an engine, motor and generator have been commercialized. HEV can be broadly classified into series HEV and parallel HEV. In both cases, all or part of the power of the engine is converted to electrical energy by the generator. Part of this electrical energy is supplied directly to the motor, and the excess electrical energy is stored in a battery. Electrical energy is supplied to the motor not only from the generator but also from this battery. The supplied electrical energy is converted to kinetic energy by the motor, and drives the vehicle.
When the energy produced by the engine passes through the generator, battery and motor, losses occur, and these losses are not necessarily small. Consequently, the parallel HEV wherein a mechanism is provided to drive the vehicle directly under the engine output and suppress these losses, has become the most popular form of hybrid vehicle.
However, if the energy consumed by the motor could be directly supplied by the generator without insufficiency or excess, the losses occurring when the battery is charged or discharged would be largely reduced, and the efficiency of even a series HEV might be improved. In JP-A-H11-146503 published by the Japanese Patent Office in 1999, a control method (referred to hereafter as synchronous power generation control) wherein the power consumed by the motor is generated by the generator without insufficiency or excess, in order to reduce the losses when the battery is charged or discharged.
However, in an HEV which performs this type of synchronous power generation control, battery charging and discharging may be performed intentionally due to the following reason.
Reason 1: Even if it is attempted to perform synchronous power generation control, it is impossible to completely eliminate excesses or insufficiencies, so the battery state of charge (SOC) must be feedback-controlled to an optimum value.
Reason 2: The synchronous power generation control will not always give the optimum fuel cost-performance under all running conditions. It may occur that under specific running conditions, synchronous power generation control may be interrupted and the battery is used.
Therefore, the following problem occurs when battery charging/discharging is performed intentionally while performing synchronous power generation control. Specifically, if the power generated is made less than the power required by the motor, the deficiency must be made up by power from the battery. However, the power which can be extracted from the battery and output to the motor varies according to the voltage which is applied to the motor, and if the generated power is reduced without considering the power which can be output, the power which can actually be output (discharged) from the battery will be less than expected, and it may not be possible to supply the motor power required by the driver.
It is therefore an object of this invention to supply a motor power required by the driver without being affected by a battery charge state, when battery charging/discharging is performed intentionally while performing synchronous power generation control.
In order to achieve above object, this invention provides a control system for a vehicle, comprising a generating device, a battery, a motor electrically connected to the generating device and battery, which drives the vehicle, and a controller which functions to determine a running condition of the vehicle, compute a target motor power, which is a target value of the power of the motor, based on the vehicle running condition, compute an available output from the battery to the motor based on the target motor power, compute a target generated power, which is a target value of the power generated by the generating device, based on the available battery output and target motor power, and control the generating device based on the target generated power.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.